1. Field of the Invention
The present invention relates to a catalyst carrier body for exhaust systems of internal combustion engines, having a configuration for temperature measurement and/or heating of walls of the catalyst carrier body.
As emissions regulations for internal combustion engines, particularly in motor vehicles, become ever more stringent all over the world, catalytic converters are increasingly being used to detoxify the exhaust gases. It is generally necessary to regulate the combustion process of an engine as a function of many measured values, as well as to monitor the functional capability and status of a downstream catalytic converter and include it in the regulation as needed. In particular, that requires temperature measurements in the exhaust system and/or in the catalytic converter itself.
The basic structure of a catalytic converter is described, for instance, in International Application WO 89/07488. That publication in particularly describes a metal honeycomb body which includes many sheet-metal layers, at least some of which are structured and one or more of which are reinforced.
The sheet-metal layers include two or more identically structured sheet-metal layers resting in contact with one another.
Various versions of honeycomb bodies made up of structured sheet-metal layers, in particular alternatingly disposed smooth and corrugated sheet-metal layers, are known from International Application WO 90/03220, corresponding to U.S. Pat. No. 5,135,794. International Application WO 89/10471, corresponding to allowed U.S. Pat. No. 5,232,672 issued Jun. 21, 1994, also discloses an electrical heating configuration for such honeycomb bodies.
Finally, Published International Application PCT/EP89/00311, corresponding to U.S. Pat. No. 5,135,794, shows various options for integrating temperature sensors into a metal honeycomb body in order to measure the temperature in it directly.
One problem in measuring temperature in the exhaust gas and especially in the interior of a catalytic converter is that the exhaust gas, at temperatures that may be above 1000.degree. C. under some circumstances, act highly corrosively, so that alloys which in principle would be well suited for temperature sensors or as heat conductors, cannot readily be used unprotected.
Another problem is that the exhaust gas flow in an exhaust system does not have a uniformly distributed profile over the cross-section of the exhaust system, so that spot measurement of temperature is generally not especially conclusive. For that reason, and as already indicated in Published International Application No. PCT/EP89/00311, corresponding to U.S. Pat. No. 5,135,794, the measurement should, if possible, be performed linearly over a representative cross-section of the exhaust system. 2. Summary of the Invention
It is accordingly an object of the invention to provide a catalyst carrier body for exhaust systems of internal combustion engines, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type, in which a configuration for temperature measurement and/or heating can be used in particular in the interior of the catalytic converter and which permits the use of arbitrary materials without consideration of their corrosion properties.
With the foregoing and other objects in view there is provided, in accordance with the invention, a catalyst carrier body for exhaust systems of internal combustion engines having a configuration for temperature measurement and/or heating the walls of the catalyst carrier body, comprising at least two layers, namely an upper layer and a lower layer resting predominantly tightly against one another and having identically structured metal foils with a thickness of from 0.02 to 0.1 mm; at least one of the layers having an outward bulge forming at least one void along the layers and between the two layers; and at least one temperature sensor and/or heat conductor extending in the void or having supply lines extending in the void.
In such a configuration, the upper and lower layers may be formed of a high-temperature and corrosion-proof material and can protect the actual temperature sensor or its supply lines. The present invention is equally suitable for both punctiform measuring sensors, having supply lines which need to be protected, and for sensors or heat conductors that measure linearly or over a large surface area, all of which must be protected. Typically, temperature sensors include a resistor wire or resistor foil, particularly of nickel alloys. So-called jacket measuring conductors are often used, in which a resistor wire, imbedded in a layer of electrically insulating ceramic powder, is disposed in a small metal-jacketed tube. The invention is especially suited to such jacket measuring conductors, but precisely because of the presence of the protecting upper and lower layers it is also possible to embed a measuring conductor directly between electrically insulating layers. A measuring conductor may be connected by its end to the upper or lower layer, so that only one electrically conducting lead has to be laid and connected, while the other connection is made by the typically present contact of the upper and lower layers to ground. In principle, however, the invention is also suitable for two-lead or even multiple-lead configurations, in particular for conductors laid in the shape of a U in a small jacket tube.
Since very thin metal foils with a thickness of 0.02 to 0.1 mm are generally used for the upper and lower layers, it is useful to form the void in which the heat conductors, the temperature sensors and the supply lines, that are all referred to below as measuring conductors, are to be laid, by bulging out both layers, so that the necessary deformations are not overly extensive. In principle, however, it is also possible to create a void in only one of the two surrounding layers by bulging outward. The configuration according to the invention can be accommodated practically in any arbitrarily structured sheet-metal layers, but it has proved to be especially suitable if the sheet-metal layers have a corrugation in which the waves have a predetermined wave height and the measuring conductor extends approximately crosswise relative to the corrugation. In order to provide for the later buildup of a honeycomb body, it is especially advantageous if the outward bulges are constructed in such a way that they do not change the wave height but instead always contact the insides of the wave. This kind of configuration can, for instance, be produced by providing that a measuring conductor is rolled-in between two metal foils by means of two intermeshing toothed rollers, in particular with involute toothing. In this process the two rollers for producing corrugated products are provided on the outside in the circumferential direction with a groove, having a depth which is approximately equal to the diameter of the measuring conductor to be rolled. This groove means a notching-in of only those teeth of the corrugated rollers that later form the insides of the corrugation. In this way, a measuring conductor can be rolled precisely in such a way that it always extends on the inside of the corrugation and thus does not affect the wave height, so that the wave combs on both sides of the corrugation do not allow the presence of the measuring conductor to be apparent. This can play a decisive role in later processing to make a metal honeycomb body.
Although in principle it is possible to roll a measuring conductor between smooth foils as well, for example using a pair of rollers in which at least one roller includes an elastic material, nevertheless this kind of smooth sheet-metal layer cannot be arbitrarily further processed well to make a honeycomb body, since the outward bulge may under some circumstances require a corresponding groove in adjacent structured sheet-metal layers as well as a smooth sheet-metal layer with an outward bulge that is more flexionally stiff than typically smooth sheet-metal layers. In contrast thereto, a corrugated sheet-metal layer with a measuring conductor is very elastic, it cannot be distinguished from a typical corrugated sheet-metal layer by its external lines of contact, and because of the corrugation, it can receive a substantially longer temperature sensor or heat conductor than a smooth sheet-metal layer, which can markedly increase the measurement accuracy or allows arbitrary resistances on the part of the heat conductor.
In order to provide long-term stability in a corrosive medium, it may be important for the measuring conductor to in fact be accommodated in a gas-tight manner between the two layers. In order to achieve this it is useful to join the layers together in a gas-tight manner, at least at their edges, and preferably to braze them. In particular, this can be achieved by rolling a thin, for instance self-adhesive brazing foil along the edges of the layers simultaneously with the measuring conductor, so that brazing can be performed in a later production step. Naturally, the upper and lower layers may also be formed by folding only a single foil, so that then only every other edge needs to be brazed.
Particularly if the layers alone or together with other sheet-metal layers, at least some of which are structured, are formed to make a honeycomb body that has a multiplicity of channels through which a fluid can flow, in any case brazing of the sheet-metal layers takes place at the end surface later, so that by means of this process alone, brazing of both of the layers that protect the measuring conductors can already be done. Once again, however, if an additional brazing foil is rolled-in jointly, the quality and tightness can be improved. As will be described in detail below in conjunction with the drawing, it is especially advantageous if the temperature sensor configuration is used alone or together with other sheet-metal layers, at least some of which are structured, to form a honeycomb body that serves as a carrier body for catalytically active material. In that case, the temperature sensor does not measure the gas temperature in the exhaust gas of an internal combustion engine but rather directly measures the wall temperature in the catalytic converter, which increases the confidence level of the temperature measurement in terms of its functional capability.
Typically, such honeycomb bodies are surrounded by a jacket tube, through which the measuring conductor must naturally be passed. This can be done according to the invention in particular through a window, which is especially advantageous from a production standpoint. The upper and/or lower layer then has an elongated connection strap, which can be passed through the window to the outside with the measuring conductor embedded in it, without impeding any production process especially.
It should be pointed out that the configuration according to the invention, while being especially well-suited to temperature measurement or heating in a metal honeycomb body, is not limited to that application. In principle, such configurations can also be used in other locations.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a catalyst carrier body for exhaust systems of internal combustion engines, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.